A review of the most significant domestic and, due to numerical superiority, foreign works on physical modelling of snow transport and snow accumulation processes, in particular, for the purpose of determining snow loads on roofs with arbitrary geometry, is presented. The existing practice of development of recommendations on assignment of snow loads in Russian laboratories is considered and critically evaluated. Comparison of do-mesticworks with scientific articles in the advanced world scientific journals and foreign regulatory documents leads to unfavorable conclusions. Recommendations on assigning snow loads, issued by Russian laboratories on the basisof extremely outdated and poorly substantiated methodology, bear a serious risk for evaluating mechan-ical safety of modern structures, for which such recommendations are developed. Recommendations are offered to remedy this current dangerous practice. The article also gives some suggestions on forming a basis for field observations of snow loads on existing roofs.
The calculation of snow loads on roofs of buildings and structures with arbitrary geometry is a complex problem, solving which requires simulating snow accumulation with acceptable engineering accuracy. Experiments in wind tunnels, although widely used in recent years, do not allow to reproduce the real full-scale effects of all snow transport subprocesses, since it is impossible to satisfy all the similarity conditions. This situation, coupled with the continuous improvement of mathematical models, numerical methods, computer technologies and related software, makes the development and future implementation of numerical modelling in real construction practice and regulatory documents inevitable. This paper reviews currently existing mathematical models and numerical methods used to calculate the forms of snow deposits. And, although the lack of significant progress in the field of modelling snow accumulation still remains one of the major problems in CFD, use of existing models, supported by field observations and experimental data, allows to reproduce reasonably accurate snow distributions. The importance of the “symbiosis” between classical experimental methods and modern numerical models is specifically emphasized in the paper, as well as the fact that only the joint use of approaches can comprehensively describe modelling of snow accumulation and snow transport and provide better solutions to a wider range of problems.
The article compares the requirements for calculating the snow load on the coatings of buildings and structures in accordance with the regulations of technically developed countries and associations – Russia, the European Union, Canada and the United States. It was revealed that in these norms the general approaches, the subtleties of calculating the coefficients, the set of standard coatings and the schemes of the form coefficient proposed for them differ significantly. This situation reflects the general problem of determining snow loads – at the moment there is no recognized unified scientifically grounded approach to determining snow loads on coatings of even the simplest form. The difference in the normative schemes of snow loads is clearly demonstrated by the example of a three-level roof.
Освещена актуальность определения ветровых нагрузок на свободно развевающиеся флаги в связи с возникшей тенденцией к соревновательному строительству сверхвысоких флагштоков, снабженных флагами огромной площади. Приведены основные научные работы, в которых предпринимались попытки исследовать сложное явление обтекания потоком развевающегося флага. Проведено сопоставление ветровых нагрузок на флаги, определенных по различной нормативно-технической литературе. В результате сопоставительного анализа выявлены существенные различия в ветровых нагрузках, определенных по различным источникам. Даны рекомендации проектировщикам.
In this paper, we study aerodynamic instability using the example of a two-dimensional problem of flow around a simplified section of a flexible suspension bridge (on the Tacoma River, USA). A direct dynamic coupled calculation was performed to determine the critical speed of manifestation of aerodynamic instability. The results obtained were compared with the results of engineering estimates presented in [40]. This example shows that to solve such problems it is possible to use the lighter des turbulence model instead of the les turbulence model and, therefore, a coarser mesh. In contrast to existing engineering techniques, direct numerical modeling of the interaction between the structure and the air flow allows one to take into account the reverse effect of the structure on the flow, as well as the mutual influence of several types ofaerodynamic instability.
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